Wireless local area network (WLAN, also referred to as WiFi) is standardized in the IEEE 802.11 standards (see e.g. IEEE Standard for Information technology—Telecommunications and information exchange between systems; Local and metropolitan area networks—Specific requirements; Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications).
The IEEE 802.11 specifications regulate the STA physical layer, MAC layer and other aspects (where STA, a WLAN entity, is taken to refer to an access point—AP—and/or to a wireless terminal, also referred to as a wireless communication device or simply a device) to secure compatibility and inter-operability between the access points and devices.
WLAN is typically operated in unlicensed bands. Thus, communication over WLAN may be subject to interference sources from any number of entities (known and/or unknown).
To deal with the interference, the WLAN technology relies on Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA). Application of CSMA/CA enables sharing, effectively and fairly, of the wireless medium among different WLAN entities and possibly even among different radio access technologies (RAT).
Application of CSMA/CA in WLAN requires that every entity that intends to send data first senses the common communication channel before carrying out a data transmission. If the channel is sensed as being free, the data transmission may be carried out as planned, while the data transmission is deferred or canceled if the channel is sensed to be busy. This approach avoids (or at least decreases) the occurrence of duplicate transmissions (i.e. collisions, often resulting in loss of data and need for retransmissions).
A WLAN entity (e.g. an access point) has a Clear Channel Assessment Threshold (CCAT, also referred to as the sensitivity threshold), which a received signal strength is compared to during the sensing process to determining whether the channel is busy or free. Typically, it is determined that the channel is busy if the received signal strength is larger than the threshold and it is determined that the channel is free otherwise.
FIG. 1 illustrates an access point (AP) 100 having four different associated devices 101, 102, 103, 104. The CCAT of the access point 100 is illustrated in terms of a sensing area 110. A signal received at the access point 100 and transmitted from a device within the sensing area 110 at a certain transmission power is typically larger than the CCAT. Hence, if any device 101, 102, 103, 104 within the sensing area 110 is transmitting, the channel is typically determined to be busy.
Configuration of the CCAT for an access point is a tradeoff between interference avoidance and channel utilization. A low CCAT value will enlarge the sensing area, thereby avoiding concurrent transmission with other WLAN entities located in a large vicinity, which typically reduces interference as experienced by devices associated with the access point and as experienced by neighboring access points and their associated devices. However, a low CCAT also reduces the possibilities for reusing the radio channel. On the other hand, a high CCAT value will result in a smaller sensing area, thereby enabling a larger extent of radio channel reuse while increasing the probability of collision. Thus, disadvantages will typically be experienced regardless of the CCAT value.
Therefore, there is a need for improved ways to configure the clear channel assessment threshold (CCAT).